Some retail stocks were among the biggest gainers on Wall Street Thursday, including Costco Wholesale Corp., which rose 2.8 percent. The discount store chain said that revenue at stores open at least a year rose 4 percent in August, or slightly faster than Wall Street’s expectations. Net sales were $7.95 billion for the month, an increase of 7 percent from a year earlier. The Wall Street Journal called Costco a bright spot in a month when many retailers’ results were below expectations.